Advanced extraterrestrial civilizations will inevitably face exponentially growing energy needs to support a burgeoning population. They will likely be driven to colonize neighboring planets or asteroids as habitable frontiers. But where else could they “plug in?”
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As I’ve written previously, a common idea has been to build a Dyson Sphere — a habitable shell that surrounds much of a star and soaks up energy. But this is a staggering engineering task involving dismantling moons or asteroids — something we’ve only seen Darth Vader do.
It’s clear to astrophysicists that nature’s ultimate “Energizer Bunny” is a black hole. That’s especially true for well-fed supermassive black holes. Weighing up to billions of times the mass of our sun, they can blaze as brilliant beacons far across the universe. Their intense gravitational field allows for total mass-to-energy conversion. Their deep gravitational well could extract enough locked-up
energy in a popcorn kernel to make a nuclear bomb blast.
An artificial black hole can conceivably be made comparatively battery-sized
for a super-civilization’s do-it-yourself project. Louis Crane and Shawn
Westmoreland of Kansas State University calculate that a one million-ton black
hole, smaller that the radius of an atom, could be fabricated in one year.
That is, if a super-civilization could first build a solar panel array having the area of Arizona to collect enough energy for building a black hole. The solar array would power a very large gamma-ray laser that would create a sphere of radiation that gains energy from its self-gravitation and then collapses. Voila! A black hole!
An entire asteroid may be needed to build such a “black hole machine,” as predicted by science fiction writer Arthur C. Clarke in his novel “Imperial Earth.”
Once the aliens built their first black hole, they could bootstrap energy production by using the hole’s raw power to fabricate any number of daughter
black holes as additional power plants.
The power plant would consist of a spherical shield around the subatomic black hole that would drive heat engines. Alien technology might even find a way to construct exotic gamma ray solar cells feeding directly off of the black hole’s radiation.
With such God-like power at hand, interstellar travel would become a practical spinoff for an adventurous alien empire. Crane and Westmorland write: “A civilization would be almost unimaginably energy rich. It could settle the galaxy at will.”
The black hole would not be as dangerous or hard to handle
as a massive quantity of antimatter — the commonly prescribed fuel for starship propulsion. Confining antimatter is a big problem. One leak and kaboom!
But a black hole confines itself. What’s more, simply making a black hole drive would require millions of times less energy than synthesizing and storing a comparable amount of antimatter.
There is any number of ways to tap the energy of the subatomic black hole to make a stardrive. High-energy gamma rays gushing from the micro black hole could be converted into electrons and positron pairs. These particles would be directed by electromagnetic fields into a collimated jet.
The black hole stardrive would have to last long enough for the interstellar mission and not evaporate away, have a mass comparable to that of the starship it is propelling, and yet be powerful enough to accelerate an exhaust to a reasonable fraction of the speed of light.
The authors dismiss the viability of other proposed stardrives based on current physics. An interstellar ramjet that sucks up tenuous hydrogen produces more drag than thrust. My favorite, laser beam propulsion transmitted from the home star, runs into the problem that the beam spreads too fast.
The authors propose that a careful search through astronomical observations of the gamma-ray sky could conceivably detect the gamma-ray exhaust from an alien starship. Even better, the black hole drive would emit high frequency gravity wave ripples in spacetime. A SETI detector could be
built to look exclusively for such unique high-pitched waves (with wavelengths shorter
that the size of an atom).
A positive detection could be evidence for E.T. The conundrum is that astrophysicists would naturally first scramble to come up with a natural, albeit exotic, explanation for the source of such a signal.
But in the absence of a viable physical alternative to such a detection, we could
someday be faced with the realization that we are not the only sentient life
with the ambition of navigating the galaxy.
Image credits: NASA, Uppsala University, John Adams Institute